The research programs of the principal user group are directed at structural studies of macromolecules, macromolecular assemblies and cell organelles such as ribosomes and plasma membranes. The major techniques to be employed center on X-ray diffraction from single crystals, solutions or partially ordered systems. In addition to the time-average structures, which are the most immediate output of such work, the programs will be particularly aimed at studying the relative motion of various parts (domains) of the polymer chains and of the subunits with respect to each other in the larger aggregates. Motion can, in part, be inferred from static structural differences under varied conditions of environment and ligation. Of special interest is the motion of specific side chains during catalytic cycles, of polymerases along their nucleic acid substrates, the translocation step of ribosomes on the message during protein synthesis and of the secretion of polypeptide chain into and through the membrane bilayer. The proposed diffraction studies require the more rapid means of data collection that will be provided by the Hamlin-Xuong two-dimensional multiwire array detector. This detector and the associated computer that is required to process the vast amount of data will increase the rate at which accurate high resolution protein crystal diffraction data can be measured by at least a factor of 10 to 20. Spectacular recent advances in cloning have made available large numbers of proteins and nucleic acids in substantial quantities. The large increase in the number of suitable crystallographic projects will be easily accommodated by this major step forward in the technology of X-ray diffraction data collection. Further, the 2D array detector will be used to study X-ray diffraction from partially ordered and disordered systems, which is a new application of this detector technology in the X-ray field.